I need to detect symbols on a drawing. I want to use following procedure:
1/ feature extraction on each symbol in the trainingset using SIFT
2/ feature extraction on the scene image
3/ compare if the symbol is detected and check rotation , scale, etc.

I got this to work with pretty statisfing result. However, some of my symbols are so simple that SIFT is unable to extract features. (i use open cv 4.10.0)
I don’t really understand, because the symbol does have some distinctive edges and corners.

The symbol looks like this:
enter image description here

I tried increasing the nFeatures parameter, change the grayscale to binary for more contrast, but no improvement.
Are there settings for the detector that i can change so multiple features are detected? Or perhaps some preprocessing on the symbol i can try?